The United States has formally handed over control of a controversial prison to the Afghan government, despite concerns about the fate of some of its inmates.

A small ceremony at Bagram prison outside Kabul Monday marked the handover of more than 3,000 prisoners from U.S. to Afghan authorities. About 600 remain in U.S. custody.

Colonel Robert Taradash said coalition forces have ensured that those who would threaten Afghanistan would not return to the battlefield.

Afghan Defense Ministry spokesman Zahir Azimi said that according to the country's law, foreigners don't have the right to keep any Afghan prisoner in the future.

Bagram Prison, Afghanistan

President Hamid Karzai hailed the transfer of the prison and the inmates as a victory for his country's sovereignty.

U.S. officials say they have suspended additional transfers because of concerns about the intentions of the Afghan government. It is not immediately clear what those concerns are, but they seem to have emerged after a meeting Saturday between President Karzai and General John Allen, the top commander of American and NATO forces in Afghanistan.

Rachel Reid with the human rights group Open Society Afghanistan says the Afghan government fears a "mini-Guantanamo" might result if the Americans get to hold third country nationals indefinitely in Afghanistan.

But a U.S. official, Deputy Public Affairs Officer Jamie Graybeal, said those so-called third country nationals are not covered in the March agreement. About 600 detainees that remain in U.S. custody were captured following the March agreement that outlined the transfer of authority to the Afghans.

Key Developments at Bagram Prison

2001: Bagram air base taken over by coalition forces2002: Bagram becomes main US detention center in Afghanistan, two Afghan detainees die at prison, leading to abuse charges against several US troops2009: US military review calls for overhaul of Bagram and entire Afghan prison system2012: Deadly protests erupt after US troops inadvertently burn Korans at Bagram

Some 50 foreign detainees, mostly from Pakistan, also are not covered by the agreement and have not been put under Afghan oversight. Afghan officials insist that all detainees captured by foreign troops must be handed over within 72 hours.

Sharon Behn is a foreign correspondent working out of Voice of America’s headquarters in Washington D.C Her current beat focuses on political, security and humanitarian developments in Iraq, Syria and Turkey. Follow Sharon on Twitter and on Facebook.